1. Field of the Invention
The present invention relates to a display device and a fabrication method of a display device, and more particularly to the electrode (including wiring) structure which is used in a display device such as an active-matrix-type liquid crystal display or the like.
2. Description of the Related Art
In a field of the liquid crystal display device, Al is often used as a wiring material since Al is relatively inexpensive compared to other metals and exhibits the favorable adhesiveness with a film made of SiNx or the like.
Further, in the field of the liquid crystal display device as a material of transparent electrodes, a film containing indium oxide such as ITO (indium tin oxide) or the like, for example, as a main component is often used.
Here, in the conventional liquid crystal display device, in some cases, the two-layered electrode structure formed of Al film/ITO film is adopted as a reflective electrode of a partial-transmissive-type liquid crystal display device or connection terminal electrodes of the liquid crystal display device.
However, when the film which contains Al as the main component (Al film or Al alloy film) and the ITO film are exposed to an alkaline developer in a state that the Al film and the ITO film are electrically brought into contact with each other, a cell reaction is generated due to the relationship of oxidation/reduction potential and hence, there has been a drawback that Al is dissolved in the alkaline developer and, at the same time, indium oxide and tin oxide of the ITO film are reduced whereby the ITO film is dissolved.
That is, when the two-layered electrode structure formed of the Al film/ITO film constitutes the reflective electrode of the partial-transmissive-type liquid crystal display device, due to the dissolution of the ITO film, the brightness spot failure is generated in a liquid crystal display panel thus lowering a yield rate of the liquid crystal display panel.
As techniques for overcoming such a drawback, there have been known methods which are disclosed in Japanese Patent Laid-open Heill (1999)-281993 (patent literature 1), Japanese Patent Laid-open 2000-180882 (patent literature 2) and Japanese Patent Laid-open 2000-216158 (patent literature 3).
In the above-mentioned patent literature 1, the following method is disclosed. That is, a protective metal film (Mo system or Ti system) is formed such that the protective metal film covers the whole ITO film and, thereafter, an Al film of one layer is formed thus allowing the electrode structure to have the three-layered structure formed of Al film/protective metal film (Mo system or Ti system)/ITO film. With the provision of this protective metal film, in a photolithography step after forming the Al film, it is possible to suppress a phenomenon in which a developer dissolves the ITO film through pin holes or the like formed in Al.
Further, in the above-mentioned patent literature 2, the following method is disclosed. On an ITO film, a protective layer formed of Al—W alloy or Al—Mo alloy and an Al film are sequentially stacked thus allowing the electrode structure to have the three-layered structure formed of Al film/protective layer (Al—W alloy or Al—Mo alloy)/ITO film. With the provision of this protective layer, in a photolithography step after forming the Al film, it is possible to suppress a phenomenon in which a developer dissolves the ITO film through pin holes or the like formed in Al.
Further, in the above-mentioned patent literature 3, the following method is disclosed. That is, by sequentially stacking an Al film and AlOx film on an ITO film, the electrode structure is allowed to have the three-layered structure formed of AlOx film/Al film/ITO film. With the provision of the AlOx film on the surface, in a photolithography step after forming AlOx film, it is possible to suppress a phenomenon in which a developer dissolves the ITO film through pin holes or the like formed in Al.
Further, as a method for forming the film, following two types of techniques are disclosed.
(A) The Al film is formed by a sputtering method using Al as a target and, thereafter, the AlOx film is formed by a sputtering method using Al containing an oxygen element as a target.
(B) Using Al as a target, the Al film and the AlOx film are formed by a sputtering method while gradually adding oxygen into an Ar gas in the processing atmosphere.